1. Field of the Invention
The present invention relates to a projection type liquid crystal display which is provided in audio visual (AV) equipment, office automation (OA) equipment, computers, etc.
2. Description of the Related Art
In recent years, with the development of advanced information society, there has been a great demand for a display having a large size as well as a large display capacity. In order to meet the demand, high precision has been advanced in a cathode ray tube (CRT) called "A Kind of a Display". In addition, in order to achieve the enlargement of the display, a direct vision type CRT with a size of 40 inches and a projection type CRT with a size of 20 inches have been developed. However, there arise problems to be solved, involving weight, and depth of the CRT along with the relaxation of the display with a large size and a large capacity.
A flat display is used for a word processor, a personal computer, etc. The flat display performs a display using a principle different from that of the CRT. Regarding the flat display, a display with high quality has been studied, which is required in a display with high vision and used for high performance engineering work stations (EWS).
Examples of the flat display include an electroluminescence panel (ELP), a plasma display panel (PDP), a vacuum fluorescent display (VFD), an electrochromic display (ECD), and a liquid crystal display (LCD). Among these flat displays, the LCD is considered to be most useful because of easiness of a full-color display and matching with a large scale integrated circuit (LSI). Thus, the LCD has been remarkably developed.
There are two kinds of LCDs: a simple matrix drive LCD and an active matrix drive LCD. The simple matrix drive LCD has a structure in which liquid crystal is sealed in an XY matrix panel, and performs a display taking advantage of the rapid response property of the liquid crystal. The XY matrix panel is obtained by disposing a pair of glass substrates so as to face each other, each glass substrate having electrodes formed in a stripe shape so that the electrodes formed on one substrate cross those formed on the other substrate. The active matrix drive LCD has a structure in which non-linear elements are directly added to pixels, and performs a display positively taking advantage of the non-linear properties (e.g., switching property) of each element. Thus, the active matrix drive LCD is less dependent upon the display property of liquid crystal itself, compared to that of the simple matrix drive LCD, and thus it enables it to create displays with high contrast and high-speed response. The non-linear element has two types: a two-terminal type and a three-terminal type. Examples of the two-terminal non-linear element include a metal-insulator-metal (MIM) and a diode. Examples of the three-terminal non-linear element include a thin film transistor (TFT), a silicon metal oxide semiconductor (Si-MOS), and a silicon-on-sapphire (SOS).
In recent years, the projection type LCD has been actively developed so as to meet the demand for more powerful images. In particular, in order to obtain an image with high quality, the projection type display such as an active matrix drive LCD has been studied and marketed positively.
FIG. 9 shows a typical example of the reflective LCD. In this reflective LCD, white light emitted from a lamp 100 is divided into red, green, and blue components by dichroic mirrors 101, 102, and 103. Lights with the respective color components are transmitted through liquid crystal panels 104, 105, and 106 for each color and synthesized to as to be an image by dichroic mirrors 107 and 108. The synthesized image is magnified by a lens 109 so as to be projected with color on a front face or a back face of a large screen (not shown).
However, the LCD shown in FIG. 9 has a problem of its large size. In order to avoid the enlargement of the LCD, it is required that the liquid crystal panels 104, 105, and 106 are made small, and optical components such as the lamp 100, the mirror 101, 102, 103, 107, and 108 and the lens 109 are made small so as to correspond to the miniaturized liquid crystal panels 104, 105, and 106, whereby the whole optical system is miniaturized. Along with the miniaturization of the optical components, it is also required to provide the optical components with high magnification. Moreover, in order to avoid a decrease in image quality caused by magnifying an image with high magnification, it is required to provide the liquid crystal panels with a high resolution.
FIG. 10 shows the relationship between the number of pixels and the numerical aperture of a current TFT-LCD. As the number of pixels increases, an LCD will have a higher resolution. As shown in FIG. 10, the numerical aperture is decreased as the resolution is increased, resulting in a dark display. In addition, in the case where the liquid crystal panels are miniaturized under the condition that the display capacity (an area which substantially contributes to a display) is constant, similar problems will arise. Moreover, as shown in FIG. 9, the conventional projection type LCD has a structure in which an optical system for color division and an optical system for color synthesis are separately disposed, so that the length of an optical path for performing the color division and color synthesis prevents the miniaturization of the LCD.
There is a strong demand for a three-dimensional projection type display. A system shown in FIG. 11 has conventionally been proposed in order to realize a three-dimensional display (S. Yano and I. Yuyama; Japan Display '89 p. 48). In the system of FIG. 11, a high-vision signal emitted from a signal source 118 for a right eye is given to a CRT 119 for a right eye equipped with a polarizing filter, and an image formed in the CRT 119 is projected on a screen 120. A high-vision signal emitted from a signal source 121 and a left eye is given to a CRT 122 for a left eye equipped with a polarizing filter, and an image formed in the CRT 122 is projected on the screen 120. In this case, light components of the images for a right eye and a left eye are polarized, and the polarization directions of the respective images are shifted by 90.degree.. A viewer watches an image displayed on the screen 120, wearing polarizing eye-glasses 123, the respective glasses having the polarization directions shifted by 90.degree., whereby the viewer can watch the image three-dimensionally. However, in this system, there is a problem in that the formation of an image is adversely influenced by geomagnetism because of the use of the CRT with high precision. Moreover, the system includes two CRTs 119 and 122 and the screen 120, so that the system is hardly miniaturized.
The three-dimensional display is also made possible in the following manner:
1) Two projection type LCDs (as shown in FIG. 9) for a right eye and a left eye are used; and PA1 an optical source for generating light; PA1 a light dividing unit which divides the light into a first light having a first polarization direction and a second light having a second polarization direction, and allows the first and second lights to come out in different directions from each other; PA1 a pair of reflective liquid crystal display elements formed of a first reflective liquid crystal display element and a second reflective liquid crystal element, each of the pair of reflective liquid crystal display elements including a pair of substrates facing each other and liquid crystal sealed between the pair of substrates, the first reflective liquid crystal display element changing the first polarization direction of the first light by the liquid crystal sealed therein to allow the first light to come out thereof, and the second reflective liquid crystal display element changing the second polarization direction of the second light by the liquid crystal sealed therein to allow the second light to come out thereof; PA1 a driving circuit for driving the first reflective liquid crystal display element and the second reflective liquid crystal display element with synchronization; PA1 a light synthesizing unit for receiving the first light which comes out of the first reflective liquid crystal display element and the second light which comes out of the second reflective liquid crystal display element, and synthesizing the first and second lights into image light; and PA1 a screen on which the image light is displayed.
2) Three liquid crystal panels for displaying an image for a right eye and three liquid crystal panels for displaying an image for a left eye are disposed in one box.
However, it is difficult to miniaturize the display.